SOIL - IT'S MORE THAN DIRT

During this activity you should be able to:

Perform a variety of procedures on known and unknown soil samples
Differentiate the soil samples based upon their physical and chemical characteristics

Part 1 - Making a Shoe Mold

Empty the soil sample you brought from home into one of the numbered plastic pans provided. Keep a small amount of the sample for parts 2, 3, and 4. Use the number on the pan to identify your sample and your mold.
Ask a member of your group or class, preferably someone wearing a runner with a distinctive tread, to step firmly into the soil sample.
Prepare plaster of paris by gradually adding calcium sulfate powder to 200 ml of water until the mixture is thick and creamy, but thin enough to pour. Stir carefully to avoid bubbles.
Pour the plaster of paris into the shoe imprint in the soil sample. Pour carefully so that the plaster of paris covers the whole impression. Avoid bubbles. Prepare more plaster of paris if necessary, but remember, the thinner the layer of plaster, the faster it will dry.
Set your impression aside to dry and proceed with the analysis of your soil sample.

Part 2 - Capillary Action of Soils

Wet a square piece or gauze and attach it to the bottom of a powder funnel using an elastic band
Measure 100 ml of water into a 250 ml beaker
Weigh out 100 g of one of the known soil samples
Place the soil sample in the funnel and pack it down firmly
Place the funnel in the beaker. Be sure the stem of the funnel reaches the water. Depending upon the relative amounts of sand, clay and humus in the sample, water will be abosrbed up from the beaker into the soil
Measure the amount of water remaining in the beaker after 5 minutes, and for every 5 minutes for 30 - 60 minutes
Place the soil sample and the powder funnel to the side for Part 4
Record and share the information about the rate of absorption of water for each of the known samples
Repeat the procedure with your unknown soil sample

Part 3 - Microscopic Examination

Obtain small samples of sand, clay and humus.
Using a stereo-microscope, make drawings of each sample
Examine and draw your unknown sample. Try to identify the sand, clay and humus in your sample

Part 4 - Water-Holding Ability of Soil

After Part 2 is completed, place the powder funnel containing the soil sample, from part 2, over the empty 100 ml graduated cylinder
Pour the remainder of the 100 ml of water in to 250 ml beaker into the soil sample
Allow the water to run through the packed soil sample
When the water has stopped running through, read the amount of water that ran through the soil sample into the graduated cylinder
Record the volume of water held (Volume held = 100 ml - volume in graduated cylinder
Keep the water in the graduated cylinder for Part 5
Repeat Part 4 procedure using your unknown sample.

Part 5 - pH

Use the water sample which passed through the soil sample in part 4 and pH paper to determine the pH of the known and unknown soil samples
If the water is coloured or clouded by soil particles, filter or centrifuge to obtain a sample that is as clear as possible.

Part 6 - Examination of the Mold from Part 1

When the plaster molds have hardened, obtain one that is NOTthe one you made
Carefully remove the mold from the soil sample
Examine both the impression and the mold to see if the mold is an accurate representation of the impression
Measure and record the length and width of the mold
Examine the tread on the mold. Note any irregularities in the mold
Using the shoes that made all the imprints, determine which shoe made the mold you examined
Using the information from the analysis of soil samples in the numbered pans, determine which sample number and which type of soil left the clearest impression.

Using the data from the capillary action of soils and your unknown soil, graph the rate of water uptake vs time for the soil samples. Find the slopes of each graph and describe the significance of each slope.
Based on the data you collected in this activity, describe the compostion of your soil (the unknown) and classify it as loam, sandy loam or clay loam.

For more information contact: lsandner@cln.etc.bc.ca